In piston engines, particularly in diesel engines, fuel is admitted into a combustion chamber of the engine by means of a fuel injection nozzle(s). Typically fuel injection nozzle comprises a needle the position of which controls the state of the injection. The tip of the needle prevents or allows the flow of the fuel from the gallery to spray opening(s) of the nozzle. The body of the nozzle comprises a fuel gallery into which a fuel conduit, usually a drilling is extending. A common principle of the operation is a spring loaded needle which is opened by the fuel pressure in a fuel gallery. When the needle is lifted against the spring force fuel from the gallery is admitted through injection orifice(s) into the combustion chamber of the engine. The needle is also guided by the nozzle body. Typically the nozzle body is attached to a nozzle holder body by means of which the nozzle is fixed to the engine.
The injection event itself has high impact on combustion of fuel in piston engine, particularly when compression ignited diesel cycle is employed. For example timing of injection start, duration of the injection has significant effect on the combustion process. Particularly the injection pressure has major impact on the formation of fuel fume and thus also on the combustion process. Publication U.S. Pat. No. 4,405,082 discloses a fuel injection nozzle in which an intensifier piston is provided for increasing the pressure of the fuel within the injector. The capability of increasing pressure is limited considerably by the physical size of the injector which is limited by the available space in the cylinder head where the injector is to be installed.
In older generation diesel engines the fuel injection takes place by an injection pump in which fuel is pressurized and delivered to each injection nozzle separately for each injection. Even if the system is reliable in operation this requires substantially long high pressure piping for each individual injector nozzle. Additionally, considering the present emission requirements, the pressure available does not result in desired injection pressure.
Hence, it is a common aim to perform the injection of the fuel at very high pressure, e.g. at a magnitude of 1000 bar and above. A common approach used in diesel engines is a so-called common rail fuel injection system. Publication EP 0959245B1 shows a common rail injection system, the provision of pressure and the injection of fuel are functionally separated from each other. Fuel is fed by means of a high pressure pump into a common pressure supply, from which it is led through separate pipes into the injector of each cylinder. Similarly in this kind of a solution high pressure piping is needed.
Another problem in the common rail injection systems caused by the continuous pressure prevailing in the system is possible leak of the injector in to the cylinder in the case of malfunction of the nozzle. Publication EP1270931B1 shows a fuel system shut-off valve which prevents the leak fuel flow into the combustion chamber by allowing only a limited amount of fuel to flow at a time.
An object of the invention is to provide a fuel injection nozzle in which the injection performance is considerably improved.